As science and technology advances, a global positioning system (GPS) originally designed for military purposes is opened to the public and commercial use now, and the American global positioning system includes 24 geostationary satellites operated in 6 orbits with an altitude of approximately 20,000 kilometers and revolving around the earth once every 12 hours so that each satellite can be assured to passes through a same point on the surface of the earth at the same time everyday so as to constitute virtual coordinates in the space.
Folks can possess and use a receiver to track all satellites of the global positioning system and immediately compute the coordinates of the location, the moving speed and time of the receiver. The principle of computing these data relies on that the coordinate of the location of any satellite in the space at any moment is taken as a known value when the satellite is in motion. The coordinate of the location of the receiver is taken as an unknown value. The time taken for sending a message from the satellite in the space to the receiver can be calculated by comparing the clock of the satellite with the clock within the receiver. The product of the time difference and the speed of the transmitted electric waves (which is generally set to the speed of light) can be used to compute the distance between the satellite in the space and a user's receiver. Therefore, a related equation can be derived from the trigonometric vector relations.
In general, the coordinates of the location of our receivers can be calculated by the aforementioned principle. A related equation will be obtained for every signal received from a satellite so that after the signals transmitted from three or more satellites are received, planar coordinates (longitude and latitude) can be further calculated. If the signals transmitted from four satellites are received, the altitude of the GPS can be found, and if the signals transmitted from five or more satellites are received, then the accuracy of the calculation will be improved.
As the GPS becomes an open system, people continue researches to enable a personal digital assistant (PDA) to be integrated with the GPS for different applications. However, traditional PDAs still require users to manually turn on or off the PDAs even though the GPS is combined, and then start the GPS for the navigation function after the PDA is turned on. Such procedure causes inconvenience to users and fails to provide a user-friendly man-machine interface.
Therefore, the inventor of the present invention based on years of experience in the related field from conducting research and experiments, invents a control system in accordance with the present invention in the hope of obtaining expected results and overcoming the shortcomings of the prior arts.